A standard filter press, such as described in U.S. Pat. Nos. 3,926,811 and 4,166,035, has a plurality of plate assemblies each constituted by a rigid support plate and a rigid frame lying on the support plate and integrally formed with a flexible central region forming a filter panel. A filter cloth overlies the frame and is supported at the central region on bumps formed on the panel. At least two such plate assemblies are joined together with the filter cloths against each other and forming a common intake chamber, each filter cloth forming with the respective panel an output chamber, and each panel forming with the respective support plate a closed dewatering chamber. Normally a filter press comprises a whole stack of such assemblies with each support plate except for the end support plates serving two assemblies and bounding two dewatering chambers.
During normal use the dewatering chamber is empty so that each panel lies against the central region of the respective support plate. A solution to be filtered is introduced into the intake compartment between the two cloths and the filtrate is aspirated from the output chamber between each cloth and the respective filter panel.
When the filter cake that builds up on the cloths becomes too thick, input of solution into the intake compartments is stopped and the dewatering compartments are filled, normally with a clean fluid compatible with the filtrate. Meanwhile the output pump continues to draw liquid out of the output compartments. This action presses the two panels very tightly together so that the two filter cakes formed on them are united at the center, pressed, and dewatered into an easily removed bulk solid.
It is necessary to disassemble such a press to replace the filter cloths and clean the knobby faces of the filter panels at regular intervals. Since clean liquid only is fed to the pressure chambers, and only occasionally, it is standard to permanently fix together the support plate and frame. This minimizes handling during disassembly and reassembly. Unfortunately the press panel is virtually the only part of such an assembly which ever fails. This means that the entire assembly must be discarded whenever a press panel wears out, something particularly wasteful when two frames and press panels are bonded to a single support plate.